1. Field of the Invention
This invention generally relates to an apparatus and method for controlling the temperature and preheat of waste oil in coperation with a waste oil burner. More particularly, the invention relates to such an apparatus and method comprised of a system control means, a temperature control means, a heat transfer assembly for preheating the oil, and a pressure relief means to eliminate nozzle drip.
2. Description of the Prior Art
For many years, various methods and apparatus have been employed to attempt to preheat oil and other combustibles to obtain proper atomization of the oil for burning. Conventional oil burners frequently use the pressure atomizing principle and waste oil burners typically preheat the oil in order to reduce the viscosity and to make pressure atomization possible.
The application of such systems and methods to heavy oil and used oil of varying types, "waste oil", has created several problems which, up until now, have not been sufficiently overcome.
The problems with prior art can best be explained in light of the properties of waste oil in general. Because waste oil has already been in use, its viscosity is generally much higher than regular and unused heavy oil and it also has a substantially higher particle and dirt content. Additionally, with today's automobile oil being predominantly multi-viscosity and containing additives and polymers to achieve multi-viscosity properties, the problems are magnified. The characteristics and properties of a medium or heavy oil are substantially changed by the additives that are introduced to render the oil multi-viscosity. As an example, the temperature at which multi-viscosity oil experiences the formation of solid carbonaceous residue, i.e. coking, is substantially reduced.
The characteristics and properties, including the viscosity, of medium and heavy oils are also substantially affected by the typical use of the oil in an automobile or other engine. The typical use of oil in engines not only breaks down and thereby increases the viscosity of the oil, but also adds a significant amount of foreign particles to the oil, such as dirt and grime.
The effect on medium and heavy oils of the multi-viscosity additives, continued high-temperature use and the addition of dirt and grime, alter the properties of the oil to such an extent that the efficient, effective, and maintenance free preheating and combustion of waste oil has until now, not been sufficiently achieved.
The temperature at which waste oil forms a solid carbonaceous residue, i.e. coking, is drastically reduced as compared to clean heavy oil prior to its use. At the same time, because of the increased viscosity from use and from the introduction of additives, dirt and grime, the waste oil must be heated to a higher temperature to obtain proper atomization. The result is that there is a very narrow temperature range which must be reached and maintained in order to obtain a sufficient viscosity to achieve proper atomization, while avoiding coking and other problems which require substantial maintenance of the system and adversely affect the performance of the burner. The high temperature limitations must be maintained not only at the nozzle, but throughout the preheater and oil feed system.
The oil burner systems represented by prior art and in the industry are designed and configured such that if or when used for waste oil, they experience coking and other maintenance problems on the heat transfer surface and along the oil path, as well as inefficient and inconsistent atomization. The solid residue not only eventually covers and corrodes the heat transfer surface of the preheat means, but also clogs the oil passageway and requires the unit to frequently be disassembled to undergo maintenance, including cleaning and replacement of parts. The solid residue formed in the coking process will also periodically partially break or flake off, and flow with the oil to the nozzle filter, which it then blocks.
The prior art and systems employed in the industry require frequent maintenance for several reasons. The first is that the actual heater element is typically positioned too remote from the nozzle, resulting in excessive heat loss in passage to the nozzle. Because of this heat loss and the target oil temperature at the nozzle, waste oil must be heated to too high of a temperature at the heater. This results in coking on the heating element as well as in the passageway.
Secondly, to obtain a high enough temperature to compensate for the heat loss of the oil in passage to the nozzle, conventional heating means transfer an excessive amount of energy per area of heat transfer surface between the heater and the waste oil. This is referred to as watt density or watts per square inch for the heat transfer area. The allowable watt density for waste oil is generally substantially lower than that for regular medium and heavy oil and is approximately eleven to thirteen watts per square inch.
Exceeding the allowable watt density for waste oil causes coking on the heat transfer surface, which gradually impinges and reduces the heat transfer to the oil and the ability to sufficiently raise the temperature of the oil. Coking is a condition which causes the need for a substantial amount of maintenance, not just on the transfer surface and in the oil passageway, but also at the nozzle.
The prior art has heretofore been unable to sufficiently reduce the coking and maintenance problems for waste oil systems. The waste oil heaters and burners in the market today have also been unable to achieve sufficient temperature control of the oil atomized at the nozzle. Insufficient or inaccurate temperature control results in insufficient atomization and incomplete combustion. The prior art utilizes unresponsive, remote and inaccurate temperature sensing devices to obtain and maintain the preferred oil temperature at the nozzle.
The failure of the prior art to maintain sufficient temperature control of the waste oil being atomized at the nozzle has led to several problems with the performance of the waste oil burner and the maintenance of the unit. First of all, if the temperature of the waste oil at the nozzle is too high, coking occurs at and around the nozzle. This substantially reduces the ability of the nozzle to properly atomize the waste oil and obtain complete combustion. The coking resulting from too high a temperature at the nozzle will corrode and clog the nozzle and require frequent maintenance and/or replacement of it. If the oil temperature upstream from the nozzle is allowed to exceed the coking temperature, then coking occurs upstream. The residue formed by coking will partially breakup during operation, causing flakes and particles to flow with the oil through the oil passageway and cover and clog the nozzle filter, which requires additional maintenance.
The inefficient and inconsistent atomization and resultant combustion greatly reduces the ability of the heater to maintain a constant, controllable and predictable heat output. This causes unacceptable temperature variation in the space heated.
If the waste oil passing through the nozzle is not at a sufficiently high temperature, it will not properly atomize or fully combust. This results in the formation of clinkers or solid carbonaceous formations in the combustion chamber, substantial wearing and destruction of the nozzle, and consequently, higher maintenance.
The industry and prior art typically utilize what is referred to as a "bi-metal snap disc thermal switch control" temperature sensor/control to monitor and control the temperature of the waste oil. These snap disc thermal switch controls typically have a 20.degree. F. control variation. The temperature variations when bi-metal discs are used is too large for an efficient waste oil system and results in what is commonly referred to as overshoot and droop. The snap discs are generally configured to activate and turn the heater off when the oil temperature reaches 10.degree. above the target temperature. However, because the temperature rise does not immediately stop, the oil coming through the passage will rise to as high as 15.degree.-20.degree. F. above the target temperature. This is commonly referred to as "overshoot", and overshoot causes coking and the many other problems discussed herein.
The typical waste oil burner in the industry today, utilizing the bi-metal snap disc thermal control, does not operate again until the oil temperature drops approximately twenty degrees below the set point temperature. The snap disc thermal control will then activate and turn the heating element on when the oil temperature drops 20.degree. below the target temperature. The temperature of the waste oil continues to drop for a period of time until the heating element has a chance to stop the temperature from decreasing and then to heat the temperaute back up to the set point temperature. The actual temperature of the oil can drop as much as fifteen or twenty degrees below the target temperature. This is referred to as "droop". Droop results in incomplete combustion, clinker buildup in the combustion chamber, excessive wear and corrosion on the nozzle and other problems discussed herein.
Another objective which must be achieved in order to greatly reduce the maintenance and increase the efficiency of a waste oil feed apparatus and preheat method is to prevent the flow of oil through the nozzle when at too low a temperature to properly atomize.
Prior art has attempted to reduce this problem by placing an inlet to complicated valve arrangements adjacent to the nozzle, including some type of structure or means for closing off the oil supply line from the nozzle. A different method disclosed by prior art for preventing the standing cold oil from discharging through the nozzle is by use of a purge line with a second pump means and a time delay valve control means to close the purge line valve on startup after a predetermined time interval. See Bears, et al. U.S. Pat. No. 4,392,810.
The problems in the industry and in prior art caused by reaching too high a temperature are greatly reduced by our new heat transfer assembly by the placement of the heat transfer assembly, controlling its receipt and distribution of heat from the heating element and its distribution thereof throughout the assembly and the resultant transfer of heat to the oil passing through the helical passageway. This has also been accomplished through the use of the temperature and system control means described in this specification.
Our invention has greatly reduced or eliminated the problem of exceeding the allowable watt density of waste oil during preheat by utilization of a helical oil passageway through an aluminum heat transfer assembly, which surrounds a cylindrical cartridge type electrical resistance heater. The distribution and transfer of heat through our heat transfer assembly and to the oil in the passageway has effectively redistributed the transfer of the heat, reduced the watt density for transfer of heat to the waste oil, and greatly reduced the coking, carbonization and consequent maintenance problems that occur in prior art and other systems.
Our invention has substantially reduced the coking and maintenance required on the waste oil feed systems, burners, and nozzles to an extent the prior art and the industry have heretofore been unable to achieve.
Our invention utilizes an anticipatory function and a rate proportional band function in its temperature controls to greatly reduce or eliminate both overshoot and droop and the problems associated therewith. Our invention also greatly reduces the temperature variation from the target temperature during the normal operating cycle, or to approximately plus or minus one degree.
Our invention is distinguished from prior art because it utilizes a simple and inexpensive control system that, upon cold startup, does not turn the fuel pump, the electrodes, or the heater fan on until the heat transfer assembly has reached a predetermined temperature, the set point temperature. During this cold startup period and before the fuel pump is energized, the standing cold oil in the heat transfer assembly is heated, which causes it to expand within the heat transfer assembly. In order to prevent this expanding oil from flowing through the nozzle, our invention includes an expansion pressure relief means which creates less resistance to the flow of the expanding oil than the nozzle and, therefore, receives the flow of expanded oil. This allows the nozzle to remain continually open while providing a pressure expansion relief means. Our invention discloses a simple, inexpensive means to prevent oil from being discharged through the nozzle on cold startup.
Our invention is distinguished from prior waste oil burners and systems individually or any combination of it by providing a method and apparatus which eliminates the problems relating to all prior art as discussed more fully herein.